Functional ear training, in one drill
A short progression establishes the key, then a note plays: which scale degree is it? That question — not "which interval?" — is the one your ear answers when you pick out a melody, because melodies are heard as degrees of a key. Each round is ten questions with instant feedback, and the visual keyboard scaffolding fades as your accuracy climbs.
Why degrees beat intervals for playing by ear
The same pair of notes feels completely different depending on where the key says home is — that felt difference is what "do, re, mi" names. Train it directly and tunes start resolving into numbers you can play in any key. Train only intervals and you get good at a quiz. This is the drill we'd tell you to start with.
Where it leads
When single notes get comfortable, the ladder continues: hear two-note motifs, then tap back whole phrases, all the way to naming real tunes. The scale degrees lesson covers the theory in five minutes, and the interval trainer is here when you want the classical companion skill.